A load such as a lamp or a motor installed in, for example, a vehicle receives a DC voltage for operation from a battery. Such a load is sometimes subjected to an overcurrent caused by circuit failure or malfunction. The overcurrent overheats and damages a semiconductor switch provided for the load as well as harness connecting the load to the battery.
To quickly detect an overcurrent and cuts a circuit between a power source and a load, various overcurrent detection and disconnection circuits have been proposed. An example of the overcurrent detection circuits according to a related art arranges a shunt resistor in wiring between a power source and a load, detects a terminal voltage of the shunt resistor, and if the detected voltage is above a reference voltage, disconnects the load from the power source.
If an overcurrent flows to the load, the terminal voltage of the shunt resistor increases. The related art detects the terminal voltage, and if the detected voltage is above the reference voltage, cuts a self holding circuit of a relay connecting the load to the power source, thereby preventing the overcurrent from flowing to the load.